The invention relates to a device used in wellbores. More particularly, but not by way of limitation, the invention relates to a downhole device used to deliver a jarring impact to objects within a wellbore.
In order to produce hydrocarbons, a wellbore is drilled until a subterranean reservoir is encountered. Once the drilling of the wellbore has been completed, a casing string may be run into the wellbore, and then cemented into place. As is understood by those of ordinary skill in the art, the subterranean reservoir can then be perforated to allow communication between the reservoir and the casing. Thereafter, the well may be completed, for instance, with the placement of gravel pack and a gravel pack screen. The well is then capable of producing the hydrocarbons.
For the drilling and completing of the wellbores to the hydrocarbon reservoirs, different types of drill and completion strings may be employed. Historically, a drill string made up of a series of coupled drill pipe has been employed for rotary drilling. Recently, coiled tubing has been utilized for both the drilling and completion phase. The coiled tubing is generally of a smaller diameter tubular as compared to drill pipe, and moreover, is continuous e.g. lacks interconnecting tool joints. It should also be understood that the invention described herein is applicable to drill pipe, coiled tubing and other types of workstrings such as wireline and electric line.
During the course of drilling, completing and producing the hydrocarbon reservoir, objects may become stuck within the wellbore. Stuck objects within the wellbores are sometimes referred to as "fish" In order to loosen these objects, jars have been developed that have the effect of providing a jolting impact to the object. Moreover, many wells being drilled include highly deviated and horizontal wells. During the course of drilling these wells, jarring impacts to the bottom hole assembly may be necessary in order to release the objects. Also, it may be necessary to set or unseat certain bottom hole assembly devices by providing jarring impacts. The invention described herein is applicable to all the above situations.
Several prior art jars have been developed. One of the first jars invented for use in wellbores was U.S. Pat. No. 2,122,751 to J. T. Phipps in 1938. Other prior art devices include U.S. Pat. No. 3,203,482 to C. R. Lyles in 1965, U.S. Pat. No. 4,333,542 to W. T. Taylor in 1982, and U.S. Pat. No. 5,139,086 to J. M. Griffith.
Despite these prior art devices, problems exist. The prior art devices suffer from not being able to accurately and dependably deliver the force required. This can result from the type of spring employed in many prior art devices. For instance, frustoconical bellville washers can flatten due to use, and the amount of force required to activate the jar can lessens with repeated use. Also, coiled springs can break, completely disrupting the operation of the jar.
Therefore, there is a need for a jar that will have dependable and reliable predetermined amount of force that will activate the jar to cause an impact force on an object in the well.